Ethylbenzene and cumene are valuable commodity chemicals that are used industrially for the production of styrene monomers and co-production of phenol and acetone respectively. Ethylbenzene may be produced by a number of different chemical processes but one process that has achieved a significant degree of commercial success is the vapor phase alkylation of benzene with ethylene in the presence of a solid, acidic zeolite catalyst, such as ZSM-5. Examples of such ethylbenzene production processes are described in U.S. Pat. Nos. 3,751,504, 4,547,605, and 4,016,218. U.S. Pat. No. 4,992,606 describes the use of MCM-22 in the alkylation of aromatic compounds, such as benzene, with short chain alkylating agents, such as ethylene and propylene.
More recently, focus has been directed at liquid phase processes for producing ethylbenzene from benzene and ethylene since liquid phase processes operate at a lower temperature than their vapor phase counterparts and hence tend to result in lower yields of by-products. For example, U.S. Pat. No. 4,891,458 describes the liquid phase synthesis of ethylbenzene with zeolite beta, whereas U.S. Pat. No. 5,334,795 describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene.
Existing processes for producing ethylbenzene, however, inherently produce polyalkylated species as well as the desired monoalkylated product. It is therefore normal to transalkylate the polyalkylated species with benzene to produce additional ethylbenzene either by recycling the polyalkylated species to the alkylation reactor or by feeding the polyalkylated species to a separate transalkylation reactor. The conversion of polyalkylated back to monoalkylated product is therefore an additional step that that adds complexity and cost to the process. Further, the quantities of impurities and heavy byproducts per unit of monoalkylate formed are typically higher in this recycle step than in the primary alkylation step.
There is a need for a process that reduces the amount of polyalkylates formed in the initial conversion of aromatics with an alkylating agent into monoalkylates, thereby reducing the amount of polyalkylates to be converted into monoalkylates and subsequent by-products inherent in that process.